Permission settings for files under Linux system

Recently there have been a lot of issues with minimizing permissions. Here is a summary of file permissions under Linux. It is actually very simple.

Before introducing the situation of files under Linux, we need to first introduce a concept, users and user groups.

Like win, Linux also requires users to log in. The difference is that in Linux, there is also a concept: user group. That is, the group to which the current user belongs. Why introduce such a seemingly useless user group? This is mainly for the convenience of team collaboration under Linux. Each user has his or her own unique permission controls. But sometimes, there are some public files or folders that you use and I use, but we don’t want everyone to be able to use them. (Anti-theft connection: This article was first published from )So the concept of a group was developed. We can add permissions only for this group. In this way, all users in this group have permission to operate this file.

Let’s take a look at the control of file permissions.

Whether it is a user or a user group, permissions only consist of three parts

Read (read): r

Write: w

##Execute: x

For example, the user permissions of file f can be set to:

rwx: represents that the current user has three permissions: read, write, and execute.

r-x: represents that the current user has read and execute permissions. (Note: Generally, execution scripts will be set to such permissions)

Remember that the order of reading, writing, and execution is fixed. If the corresponding permissions are not available, use - (horizontal line) replace this bit).

For computer users, if there is data in a location, We usually use 1 instead, if not, use 0 instead.

Therefore:

r-x is equal to 0b101. After conversion, it is 5

rwx is equal to 0b111 is 7

after conversion ---equal to 0b111 after conversion is 0

And the file permissions, as shown below, consist of three aspects Setting:

Permissions of the user to whom the current file belongs.

#Permissions of the user group to which the current user belongs.

Permissions of other users.

Note that the order of the three is also fixed.

As shown above, the total permissions of the current file are

r- -rw-r-x, converted into numbers is 4 (r--) 6 (rw-) 5 (r-x)

Generally speaking, a file has 777 permissions, which refers to the The user, the user group to which he belongs, and other users all have rwx permissions.

File Permissions

The content displayed in ls

-l is as follows:

-rwxrw-r‐-1 root root 1213 Feb 2 09:39 abc

- 10 characters determine what different users can do to the file

- The first character represents file (-), directory (d), link (l)

- The remaining characters are in groups of 3 (rwx), read (r), write (w), execute (x)

- The first group rwx: The permissions of the file owner are read, write and execute

- The second group rw-: The permissions of users in the same group as the file owner are read, write but not execute

- The third group r--: The permissions of other users who are not in the same group as the file owner are read but not write and execute

It can also be expressed as numbers: r=4, w= 2, x=1 Therefore rwx=4+2+1=7

- 1 represents the number of connected files

- root represents the user

- root represents the location where the user is located Group

- 1213 represents the file size (bytes)

- Feb 2 09:39 represents the last modification date

- abc represents the file name

Command to change permissions

chmod changes the permissions of a file or directory

chmod 755 abc: Grant abc permissions rwxr-xr-x

chmod u=rwx, g=rx, o=rx abc: Same as above u=user permissions, g=group permissions, o=other user permissions in different groups

chmod u-x, g+w abc: Remove user execution permissions for abc, add Group write permission

chmod a+r abc: Add read permission to all users

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